*2.2.1. Chemical treatments*

There are two major biologically relevant valence states for chromium, hexavalent and trivalent, with the hexavalent forms considered more potent than the soluble forms. This study focused on the hexavalent form because the marine environment favors the hexavalent form [5]. Moreover, the total Cr levels in the whales were found to be high and considering that Cr(III) is poorly absorbed by mammals [6], for the whales to accumulate these levels of total Cr, the original exposure to Cr would almost certainly have been to Cr(VI).

We treated whale cells with both a water soluble (sodium chromate) and a water-insoluble particulate (lead chromate) to determine its ability to induce DNA damage. The concentration units for the two chemicals are different (uM for sodium chromate and ug/cm2 for lead chromate) because sodium chromate dissolves fully in water and thus is a solution, while lead chromate does not and instead forms a slurry of particles in water. The cells were treated with this slurry of intact particles. Since all the lead chromate is not dissolved to express it in units of molarity would overestimate the dose. Thus, its units are weight per surface area.
